UARS re-entry Update (and Nanosail-D, and IGS 1B)

UARS update: It seems that the re-entry moment for UARS, the defunct NASA Upper Atmosphere Research Satellite, is moving forward in time, as Harro Zimmer pointed out on the Seesat-L list.

NASA and SSC Space-Track both settle for a decay on or near 24 September, and so do independant analysis by Harro Zimmer as well as my own assessment (using Alan Pickup's SatEvo software with current 10.7cm flux values).

As the orbital development near decay is highly influenced by solar activity, there currently is an uncertainty of possibly up to a few days in these predictions. Yet it seems save to say that UARS has not much more than a week left.

Nanosail-D update: Meanwhile, that other NASA object up there slowly coming down, NASA's experimental solar sail Nanosail-D, seems not quite willing to give up. It's current orbit and current values for 10.7cm solar flux suggest it will hang on at least another month, untill late October. Same caveats as for UARS apply.

IGS 1B update: this defunct Japanese spy satellite which is steadily coming down (see earlier post here and earlier posts linked their in) since it malfunctioned in 2007, likewise seems intend on spending some more time up there. The current orbit plus solar activity now give a nominal re-entry prognosis for early 2013 instead of 2012. This date is certainly still going to shift back or forth considerably however, depending on how solar activity develops.

Nanosail-D: a pattern in the Chaos

Earlier I reported on my August 14 observations of the experimental Solar sail Nanosail-D (2010-062L), including a brightness variation diagram derived from one of the images.

Initially, I could not see any clear pattern in it, so I called it "irregular". Next, Alain Figer from France pointed out it was not so irregular after all. His own images from August 16th (URL's here) show a very neat pattern of one major flash, then two secondary flashes, then a major flash again. On his images, the major flashes are 0.73 seconds apart.

Going back to my observations, it turns out it is indeed possible to find a similar periodicity of 0.73 +/- 0.03 seconds. The secondary flashes appear to be 0.73/3 = ~0.24 from these main peaks: in other words, main and secondary peaks fit a ~0.24s pattern.

Below diagram shows it. the lowest line gives the observed peaks, with the red triangles representing the main 0.73s cycle. The yellow tringles point out several secondary maxima at ~0.24s after the main cycle peak; the grey/white triangles point at a hint of a similar pattern ~0.24s before he main cycle peaks.
The upper line shows the modelled behaviour: a main peak (black triangle) each 0.73s, with secondary and tertiary peaks at ~0.24s intervals.

click diagram to enlarge

Nanosail-D flashing rapidly and brightly

As in late May and early June, Nanosail-D (2010-062L), the experimental NASA Solar Sail is making favourable passes again and under favourable conditions becomes bright and is flashing rapidly.

Yesterday evening around 22:50 local time (20:50 UTC) I observed it when it made a near-zenith pass, from SW to NE. While ascending and going through the zenith it was quite bright and an easy naked-eye object, reaching mag. +1.5. It was rapidly and very irregularly, rather nervously flashing.

I shot four images, two of which are shown below: in the first image, the brightness variation is photographically less apparent than it was visually, because the trail is near saturation. It shows the Solar sail passing just below Lyra (Vega in top left) along with a stray, the French Optical Remote Sensing satellite Spot 4 (98-017A, the fainter of the two trails).

The second image, shot while Nanosail-D was getting fainter, shows the sharp flashes more readily.

click images to enlarge

From the latter image, I could derive this brightness variation diagram:

click diagram to enlarge

A large number of sharp brightness peaks can be seen: I count some 26 peaks in a 10.05 seconds time span, the one more prominent than the other. No regularity in the pattern is apparent.

NanoSail-D: a brief note on how I construct these brightness curves

Some people have asked me how I get the brightness curves from my images. So here is a brief explanation.

On each image, the satellite has made a trail. Start and end times of the exposure are well known, and the start and end of the trail corresponds to these times.

Next it is as simple as using software (e.g. MaximDL, or IRIS) that can read pixel values along a line: let the software read a line that corresponds to the satellite trail on the image! With MaximDL or IRIS, this is as simple as drawing a line over the screen with your mouse, exactly over the satellite trail. The software then reads the pixel values along this line. The resulting data can be exported as a data table.

These data are then read into a spreadsheet I created, that for each data point interpolates the corresponding time (remember that the time of the first and last datapoint in the dataset is known: start and end of the exposure).

Now, this assumes the movement of the satellite on the image is linear. Strictly speaking, the apparent speed of the satellite is not linear. However, with short exposures (10s) that will not be a really big source of error.

NanoSail-D: evolution of the flash pattern during a pass

Yesterday evening at 23:00 CEST I observed a twilight pass of the experimental NASA solar sail NanoSail-D again (see earlier and later observations here).

This pass allowed me to capture a series of brightness curves, which document the evolution of the flash pattern during a single pass, as the looking angle is changing (looking "edge on" aroudn culmination, and then more and more "on the tail"as it is descending) . The change in flash pattern is profound: this is clearly a very complex matter where the flash pattern highly depends on the relative position of the object to the observer.

click images to enlarge

It starts (image and diagram 1) with a lot of irregular flashes, spaced 0.3 - 0.9s apart (average 0.49s but with large standard deviation).

Next (image and diagram 2), a nice semi-regular sinusoid pattern develops, flashes spaced 1.24 - 1.45 s (average 1.33s)

Then (image and diagrams 3 and 4), the period increases, the pattern transforming to a slower sinusoid with peaks first 5.61s apart, then somewhat decreasing again to 4.11s apart (edit: or maybe not: the firts "peak"might be a sub-peak. The valleys seem at similar distance to the previous diagram). Superimposed on this, a shorter cycle of minor subvariation can be suspected, with various periods.

This slower variation in the last two diagrams is why Bram, me and some other observers got the impression, on this and some past passes, of the period almost "disappearing" when NanoSail-D was descending on altitudes of ~35 degrees.

Two of the trail images in a bit more detail: note the difference in flash pattern:

click images to enlarge

NanoSail-D Galore

Yesterday evening, I observed a twilight pass (sun at -7 degrees altitude and a still bright blue sky) of NanoSail-D, the NASA experimental solar sail (see earlier posts here). It passed at 44 degrees in the east, and after culmination became very bright again, flashing to mag. 0.

Because of the bright twilight sky I had to tone down the ISO to 400 and diaphragm to F4.0. The images show the flashing behaviour very neatly, and I obtained two spectacular sinusoid brigthness curves (the second one is from the image shown):

click images to enlarge

The flash period is definitely slightly variable, varying between 1.2 and 1.5 seconds with an average of 1.35 +/- 0.12 seconds.

With the current orbit, decay is projected for mid-August.

note added: click the 'Nanosail-D' label below to see later posts on NanoSail.

Yet more bright NanoSail-D, and an unidentified object from the same launch

Yesterday evening (Wednesday evening) was very clear and saw another fine pass of NanoSail-D (10-062L), the experiental NASA solar sail. As on previous occasions, it became very bright after culmination, while descending to the southern horizon: reaching an easy naked eye magnitude of +0.5. It is still flashing, but trail saturation on the images meant I could not get a reliable brightness variation curve this time. Below are two images: one that shows it just north of the Coma Berenices star cluster, the other shows it passing south of Bootes into Virgo somewhat later (bright star in the top is Arcturus):

click images to enlarge

Tonight (Tuesday evening) I had another pass, a low west pass at 35 degrees altitude this time. And....it was invisible, to the naked eye at least.

On April 27th, Russell Eberst observed an unidentified object that moves in the same orbital plane as NanoSail-D and appears to be "something" from the same launch (see also here). It was subsequently observed by a number of other observers (and perhaps earlier, on March 3, by Greg Roberts), and yesterday I photographed it:

click image to enlarge

Another object observed this evening was Lacrosse 5 (05-016A).

More flashing NanoSail-D, and flaring KH-12 USA 224

A week after my May 24 observations, I observed NanoSail-D (2010-062L) again, the experimental NASA solar sail.

NanoSail-D (image: NASA/MSFC)

As a week ago, it became very bright after culmination, while descending in the south, and was rapidly flashing again. It was easily seen by the naked eye, reaching mag. +1 or possibly +0.5.

In fact it is so bright, that the pixel brightness of the trail reached saturation on two of the three images. The first image (below) did yield brightness information: the resulting curve is shown beneath it. The flash period is irregular, but periods of 0.5s and 1.0s pop up frequently in the diagram (for actual determined flash times, see here. Astrometry on the satellite itself can be found here).

click images to enlarge

As can be seen on the images, the satellite was in a race with an untimely field of clouds (the orangish streaks in the images), staying just ahead of it. Visually, the brightness fluctuation was much more apparent than it is on these images (due to the saturation of the latter): it was very clearly flashing.

Nanosail-D was not the only object flashing. USA 224 (11-002A), the new KH-12 Keyhole launched on January 20 this year, flared too, while passing through the zenith, with flares at 23:48:27.3 and 23:48:31.8 UTC (May 31). The "saddle" and elevated brightness between the two flares is interesting (the trail is notably fainter before the first flash, and subsequent images show it is fainter again after the second flash):

click images to enlarge

This was the second time I imaged USA 224 (The first time was May 24). In addition to USA 224 and NanoSail, I also imaged another KH-12 Keyhole, USA 161 (01-044A), and a Lacrosse SAR, Lacrosse 3 (97-064A).

Nanosail-D: a spectacular show of bright flashes!

Last night I finally was able to capture Nanosail-D (10-062L), the NASA experimental solar sail. It put on a spectacular show, flashing rapidly, becoming an easy naked-eye object after culmination when it reached magnitude +1.

As it gradually brightened from invisibility to naked-eye brightness while passing at 61 degrees altitude due east, it initially flared rapidly, in an irregular pattern, at a rate of 1 to 3 flashes per second. below is the first image, and two other where the trail runs out of the image frame (in haste, I aimed badly when repositioning the camera):

click images to enlarge

When it descended towards the South-Southeast, it became brighter, reaching mag. +1. The flashing pattern became somewhat more regular and slowed down to about one flash per 1.6 seconds. On the image, the trail is quite saturated and hence the brightness variability on the image below is less apparent than it was visually. Visually, the objet was clearly "winking", very cool to see:

click images to enlarge